Use 'new' expression in places where the type is evident for content (#2590)

* Content.Client

* Content.Benchmarks

* Content.IntegrationTests

* Content.Server

* Content.Server.Database

* Content.Shared

* Content.Tests

* Merge fixes

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Client/Administration/ClientAdminManager.cs

@@ -17,7 +17,7 @@ namespace Content.Client.Administration
         [Dependency] private readonly IClientConGroupController _conGroup = default!;
 
         private AdminData? _adminData;
-        private readonly HashSet<string> _availableCommands = new HashSet<string>();
+        private readonly HashSet<string> _availableCommands = new();
 
         public event Action? AdminStatusUpdated;